Chemical-mechanical polishing (“CMP”) processes are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, field emission displays, and many other microelectronic substrates. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting substrate to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, gate oxide layers, conductive layers, and layers of metal or glass, etc. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps.
In a typical CMP process, a wafer is mounted upside down on a carrier in a CMP tool. A force pushes the carrier and the wafer downward toward a polishing pad. The carrier and the wafer are rotated above the rotating polishing pad on the CMP tool's polishing table. A polishing composition (also referred to as a polishing slurry) generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing composition typically contains a chemical that interacts with or dissolves portions of the uppermost wafer layer(s) and an abrasive material that physically removes portions of the layer(s). The wafer and the polishing pad can be rotated in the same direction or in opposite directions, whichever is desirable for the particular polishing process being carried out. The carrier also can oscillate across the polishing pad on the polishing table.
Polishing pads used in chemical-mechanical polishing processes are manufactured using both soft and rigid pad materials, which include polymer-impregnated fabrics, microporous films, cellular polymer foams, non-porous polymer sheets, and sintered thermoplastic particles. Non-porous polishing pads are desirable for use in polishing a variety of substrates; however, non-porous polishing pads typically have a polishing surface, which has no intrinsic ability to transport slurry particles (see, e.g., U.S. Pat. Nos. 5,489,233 and 6,203,407). Accordingly, these solid polishing pads must be modified with large and/or small grooves that are cut or molded into the surface of the pad so as to provide channels for the passage of slurry during chemical-mechanical polishing. For example, U.S. Pat. Nos. 6,022,268, 6,217,434, and 6,287,185 disclose solid polishing pads comprising a polishing surface that purportedly has a random surface topography including microaspersities of a dimension of 10 μm or less that are formed when solidifying the polishing surface and macro defects (or macrotexture) of a dimension of 25 μm or greater that are formed by cutting.
Porous polishing pads typically have an inherent surface texture that can absorb and/or transport slurry. As such, porous polishing pads often can be used in polishing without the need for forming grooves on the surface of the polishing pad. Porous polishing pads can contain closed cell pores or open cell pores. Typically, the pores are spherical or nearly spherical pores, although some polishing pads comprise elongated pores that are oriented normal to the plane of the polishing pad (see, e.g., U.S. Pat. No. 4,841,680). While porous polishing pads offer many advantages over solid polishing pads in terms of cost and simplicity, porous polishing pads often do not have the most desirable physical properties (e.g., hardness, low compressibility) for certain polishing applications.
Accordingly, there remains a need for polishing pads that can provide effective planarization with satisfactory polishing efficiency and slurry flow across and/or within the polishing pad, that can be produced using low cost production methods, and that require little or no conditioning prior to use. The invention provides such a polishing pad. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.